Vantec's "Stealth" 420W Power Supply

A new piece of equipment was recently added to SilentPCReview's test bench. It is the DBS-2100 load tester, made (in Taiwan by D-RAM Computer Company) specifically for testing computer power supplies. The machine consists of a large bank of high power precision resistors along with an extensive selection of switches on the front panel calibrated in Amps (current) and grouped into the 5 voltage lines: +5, +12, -12V, +3.3, -5, +5SR. Leads from the PSU plug into the front panel as well. It is shown above with leads from the Vantec 420A plugged in.

Readers of previous power supply reviews are aware that pushing PSUs past 100W DC power output could not be achieved with our PC systems. This limitation is a thing of the past, as the DBS-2100 load tester enables simplified, controlled PSU load testing from as little as a few watts to a rated maximum of 614W.

The DBS-2100 is equipped with 2 AC outlets (individually fused with 7A 250V fuses) and 4 exhaust fans on the back panel. A bypass switch on the back panel toggles the fans on or off so that noise measurements on the PSU can be made. The resistors get very hot under high loads, so it is important not to leave the fans off for long. Note in the photo below that the Kill-A-Watt AC Power Meter is plugged into the AC outlet on the side of the DBS-2100 so that the AC power draw of the PSU can be measured.

Test Setup

The load tester allows the PSU to be tested by itself outside a case independent of any system or case, making the work flow much more smoothly. Because the load can simply be "dialed" in, there is no need to stress a PC with benchmarks in order to increase the PSU load.

The 12V (P4) lead, the 4-pin connectors closest to the PSU on each of the 3 peripheral component lines, and the main ATX connector from the Vantec 420A were all plugged into the front panel of the load tester. Using as many lines as possible helps to minimize any potential voltage drop through cables and connectors.

*NOTE about Room Temperature: For comparisons against the data in our other PSU reviews, please remember to factor in any ambient temperature differences. The test environment is not air-conditioned.

Noise Measurements

The Heath AD-1308 is a portable half-octave Real Time Spectrum Analyzer with sound level meter (SLM) functions. Below 40 dBA, its accuracy is poor, limited to 3 dB increments, down to 23 dBA. Some 15 years old, this LED-based unit has long since been displaced by digital devices with better interfaces to PCs. (Shown on page 3 of the Seasonic PSU review.) The "A" weighting was used; it most closely approximates the frequency response characteristics of human hearing.

The microphone on the sound meter was positioned about an inch to the side of the PSU fan exhaust to avoid fan turbulence in the microphone itself. The dBA obtained here cannot be compared to any other measurements due to the lack of adherence to a repeatable standard and the uncontrolled reflective environment.

No effort was made to change acoustics in the lab, which is a spare kitchen measuring 12 by 10 feet, with an 8 foot ceiling and vinyl tile floors. The acoustics are quite lively. The PSU was placed on a piece of soft thick foam to prevent transfer of vibrations to the table top.

Temperature Measurements

A DigiDoc2, obtained from San Jose based web retailer SVC, was used to read the ambient air temperature near the PSU and in the PSU itself. A thermal probe was wedged into the heatsink on which the PSU thermistor is bolted.

Heat Source

In previous reviews, because the PSU was installed in a low-airflow PC system that was being stressed, the PSU temperature was affected by the heat dissipated by the CPU and other components in the system. To simulate the increased air temperature of the PC system components in a case, a 60W or 100W bulb in a gooseneck floor lamp was placed directly over one of the PSU intake fans. The extra heat affected fan speed (and noise) as well as PSU temperature; both are shown in the table below.

Measurements

LOAD

Min Power (W)

Med Power (W)

High Power (W)

Excessive Power (W)

+5V

5

20

125

180

+12V

12

36

162

192

-12V

1.2

3.6

8

8.

+3.3V

3.3

26.4

66

79

-5V

0.5

1

4

4

+5VSR

0.5

2

8

8

Total DC Power

22.5

89

373

471

Total AC Power

40

124

540

725

Efficiency

56%

72%

69%

65%

Temp / Noise*

24° C / 50 dBA

32° C / 52 dBA

54° C / 69 dBA

63° C / 73 dBA

Temp / Noise* w/ lamp

-

36° C / 57 dBA, 60W lamp

62° C / 74 dBA, 100W lamp

74° C / 75 dBA, 100W lamp

* All noise readings were taken within 1" from the edge of the outside fan (out of the airflow path), with the fan speed switch on the PSU back panel set to "A".

Too Loud Even at Minimum Load

The Vantec 420A PSU sample started at a noise level of 50 dBA, which is ~10 dBA higher than any of the PSUs reviewed here so far. It also maintained a temperature of just 24° C, at least 10° C cooler than any previously reviewed PSU.

The "A" setting of the fan control switch seemed to be the quietest. The M setting appeared to turn all the fans to their highest speed, although the voltage to the CPU-facing fan dropped from ~5.5V to ~2V (when the PSU was run at a modearte load). The L setting usually seemed to bring the fan speed down to about the A level.

An attempt was made to measure the voltages of the 3 fans, but abandoned because of the difficulty of tapping into the various fan output connectors while keeping the fans connected. (I don't need yet another high voltage DC zap!). There was also little point.

The quietest setting of this PSU with the lowest possible load is twice as loud as the Seasonic, Zalman or Q-Technology PSUs. It is also considerably noisier than the Antec True Power series. It is louder than the noisiest units in the SPCR recommended PSU list, the 2-fan Enermax and SH models.

Louder at Simulated Typical Desktop Full Load

The Medium Load of ~90W DC power was chosen because this was the maximum sustained power level achieved with the test PC system in previous PSU reviews. Again, the Vantec's temperature remains very low in comparison but as the fans have speed up, also becomes even noisier especially with the in-case simulation of the 60W light bulb. Calculated efficiency at 72% was quite good. The line voltage regulation remained well within the +/-5% spec at this power load.

Still louder on High Load

With the in-case simulation of the 100W light bulb and a total DC power draw of 373W, temperature and noise jumped up as expected. 62° C is pretty hot, and the 74 dBA measurement does reflect a very high noise level. Still the PSU remained stable for well over 5 minutes under this load, which is far higher than it is likely to encounter in even the most fully loaded powerful desktop systems. The line voltage regulation again remained within the +/-5% spec.

An Accident on Excessive Load

This power load is excessive because the PSU blew with a loud POP! after a few minutes on this setting. The total load was meant to be ~420W, the rated capacity of the VAN-420A, but one additional 8A switch on the 12V line was inadvertently turned on, bringing the total to 471W instead. In less than 5 minutes, the 7A-250V fuse in the AC line output of the load tester blew simultaneously with something inside the PSU, bringing sudden silence to the room. It was an unfortunate accident.

The total overload was ~50W or 11%. It is surprising that the PSU did not shut itself down for self-protection. Vantec cites a number of protections -- against over-voltage, over-current, and short circuit. Section 3.10.1 of the Vantec VAN-420A Specification document specifically states:

"The PSU DC outputs are protected from supplying output current above the maximum ratings... and when output power is between 110-150%... all DC outputs are latched off in the event of an over-current event on any of the DC outputs."

The PSU was unplugged and cooled for an hour with the aid of a large powerful house fan. It was then reconnected to the load tester and set up for very low output. Upon turn-on, a loud BANG ensured from the PSU, and the AC line fuse blew again. It seems like a permanent short condition exists somewhere inside the PSU, which I believe can be declared a casualty at this point.

The Vantec 420A is the noisiest PSU we've encountered so far. Within its power limits, other aspect of its performance all fare very well, despite such concerns as the additional contact resistance of the ATX extension cable. As alluded to earlier in this very long review, the product is not appropriate for anyone interested in a quiet PC. On the desktop front, it is better suited for heavy-duty overclockers, perhaps with multiple-processor machines, obsessed with the fastest and the coolest. The 3 fans do keep things considerably cooler than quieter PCs, at least up to a point.

The Vantec 420A's ideal market segment may be that for servers. The 420A has the capacity to be used with any of a long roster of server motherboards. In server systems, the additional airflow of the 3 fans is likely welcome and the high noise level is not much of an issue. Still its desktop form factor may not be desirable for such use. All in all, the Vantec 420A, in our opinion, suffers some identity confusion.

For readers drawn to this model by association (Stealth, remember?) and the ad copy promise of reduced noise, we suggest you look elsewhere. For those seeking a powerful PSU with high airflow for a hot, powerful desktop PC -- never mind the noise! -- the Vantec 420A may be just the thing for you.

It really is too bad that one of the 420A samples became the first casualty of our new PSU load tester. Hopefully we have learned our lesson and will handle both PSUs and the D-RAM load tester with more caution and care in the future.

Our thanks to Vantec Thermal Technologies, Inc. for the review samples and their kind support. And thank you, Jim Day, for actively initiating contact between Vantec and SPCR!